1998 Chevrolet Silverado Engine Problems

JAMES3980

MEMBER
1998 CHEVROLET SILVERADO
5.7L
V8
4WD
AUTOMATIC
309,000 MILES

My engine vibrates well driving up hills then the RMP shoots up to 3 RPM then idles high till I get to level ground and drive for 2-5 kms before it starts idling normally. I have already changed the fuel filter, fuel pump, spark plugs&wires, distributer cap&rotor, coil, throttle position sensor and O2 sensor bank 1 sensor 1. No improvement after all changes. Why would that be?

6 Replies

HOMER1967

MECHANIC
875 POSTS

That is a pretty common issue on those motors, especially high mileage ones. The most likely cause is a vacuum leak at the lower intake manifold, but I could not rule out valve damage or severe carbon on the valves.I would have the intake checked first and if no leaks are found then have the engine health checked or try to do a decarbonization treatment on it.

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Saturday, February 21st, 2015 AT 6:33 PM

JAMES3980

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17 POSTS

That makes a lot of sense I will try that. Kind of weird none of that showed up on the DTC test, just everything that I have already replaced. But very useful information thank you.

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Saturday, February 21st, 2015 AT 7:30 PM

HOMER1967

MECHANIC
875 POSTS

You are welcome, a leaking intake can cause a lean code such as p0171 or p0174, but it could also cause misfire codes due to fuel deprivation of one or more cylinders possibly all on the same side. And also severe carbonization of the motor could cause misfire codes to by not letting the valves close all the way. Was it miss fire cods that you got?

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Saturday, February 21st, 2015 AT 7:43 PM

JAMES3980

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17 POSTS

Only codes that showed up was the throttle position sensor, O2 sensor bank 1 sensor 1, P1133 which has to do with the O2 sensor that I have changed and the other code had to do with the coil and I changed that to. I just changed the IAC valve to, the engine light went out after that but still same symptoms and no more codes showing up so going to have to bring my truck to the shop and get them to check for vacuum leaks and valve damages. If that don't work then not sure what to do next.

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Monday, February 23rd, 2015 AT 10:36 PM

JAMES3980

MEMBER
17 POSTS

So I just got my truck out of the shop, they inspected the valve and searched for vacuum leaks everything was good there. DTC test showed a random misfire so they changed my spark plugs cause I just had cheap ones on it. Brought my truck for a test drive up a hill and noticed right away started doing same thing from before. I brought the truck back told them still having same problems he suggested I change the K&N mass air flow tube back to the stock one because the one on it now is not sitting on the throttle body properly, he said that would cause a random misfire from not having that installed properly. Thought I get your opinion on that information that guy gave me.